Photo/electrocatalytic ammonia synthesis has recently developed fast while the ammonia yields over state‐of‐the‐art photo/electrocatalysts are still very moderate. Such low concentration of synthesized NH3 brings about a challenge to the reliable quantification of the product in photo/electrocatalysis. Notably, we found that the quantitative detection of ammonia concentration below 0.2 ppm is error‐prone, which is likely the case happening in the majority of photo/electrocatalytic NH3 synthesis, thus arising concerns about the rationality and accuracy for low‐concentration ammonia quantification in these processes. Herein, we discuss the methodology used and analyze the reliability of various detection methods for the detection of trace ammonia in aqueous media. The challenges facing the detection of low concentration of ammonia in photo/electrocatalysis can be overcome by integration with multiple detection methods. According to the data presented, we also propose an effective criterion for precise quantification of ammonia, avoiding the unreasonable comparisons in photo/electrocatalytic ammonia synthesis. The analytical methods for the detection of ammonia concentration below 0.2 ppm in photo/electrocatalytic N2 fixation are evaluated rigorously, reliably, and insightfully. The low‐concentration ammonia quantification minefield was indicated and a rigorous ammonia detection flowchart as well as another reference standard to achieve a more accurate and responsible ammonia detection in photo/electrocatalysis was concluded.